1. Field of the Invention
The present invention generally relates to the separation and disposal of an undesired heavier fluid, such as water, from a desired lighter fluid, such as oil and/or gas, below ground surface in a production well and, more particularly, is concerned with an above production disposal tool which disposes an undesired heavier fluid, such as water, in a disposal formation above a production formation.
2. Description of the Prior Art
In addition to producing a desired lighter fluid, such as oil and/or gas, production wells also often yield substantial quantities of an undesired heavier fluid, such as water (including salt water). Co-produced undesired fluids must be separated and properly disposed of; however, the cost of handling and disposing of undesired fluids is significant and therefore impacts the economic feasibility of production wells, especially marginal wells.
Traditionally, undesired fluids have been pumped to the surface along with desired fluids then separated from the desired fluids and transported, often by truck, to another location where they are pumped down a separate well into a subterranean disposal formation. This "surface approach" is inappropriate for many production wells not only because it is very costly, but also because it raises the potential for adverse environmental impacts due to the possibility of an inadvertent escape of undesired fluids during transport and disposal.
Alternatively, undesired fluids can be separated from desired fluids in the production well below ground surface and pumped into a disposal formation without ever bringing the undesired fluids to the surface. This "in-situ" approach eliminates the need to transport the undesired fluids to a separate disposal well, thereby reducing disposal costs and reducing the environmental risks associated with disposal of undesired fluids. The "in-situ" approach, however, requires the availability of an appropriate disposal formation.
U.S. Pat. No. 5,425,416 to Michael N. Hammake et al, assigned to the assignee of the present invention, discloses a down-hole injection tool for down-bore in-situ disposal. This particular tool accomplishes the "in-situ" disposal of undesired fluids, but it requires the availability of a disposal formation below the production formation into which the undesired fluids can be injected. Many times, a disposal formation is not available below the production formation because one does not exist or, as is more often the case, the well bore and casing are not of sufficient depth to reach a disposal formation below the production formation and it is cost prohibitive to extend the well bore and casing. Nevertheless, in many production wells, appropriate disposal formations are available above the production formation and undesired fluids may be transferred from the lower production formation into the upper formation via the existing well bore to accomplish "in-situ" disposal of the undesired fluids.
Assemblies exist that are capable of transferring fluids from a lower formation to an upper formation. One example is disclosed in U.S. Pat. No. 3,170,520 to Arutunoff. The dual-flow transfer assembly disclosed in the Arutunoff patent may be utilized to introduce fluids produced in a lower formation into an upper formation. However, the Arutunoff assembly does not provide separate passageways for the movement of desired fluids, such as oil and/or gas, and the movement of undesired fluids, such as water. Thus, it is not capable of simultaneously bringing desired fluids from a lower production zone to the surface and disposing of undesired fluids from the same lower production zone in an upper disposal formation.
Consequently, a need still exists for a tool which may be utilized to simultaneously accomplish delivery of desired fluids from a production formation to the ground surface and "in-situ" disposal of undesired fluids produced in the same production formation into a disposal formation above the production formation.